[R] a^c(1:3)

[Dimitris Rizopoulos]

"^" is vectorized operator, so

a^c(2,3)

is essentially the same as

a^rep(c(2,3), length.out = length(a))

which is

c(a)^rep(c(2,3), length.out = length(a))

but put back in a matrix format (i.e., with rows and columns).

Now, if you want each column in different power, you need to explicitly 
use rep(), e.g.,

a^rep(c(2,3,4), each = nrow(a))


I hope it helps.

Best,
Dimitris


On 9/7/2010 6:35 PM, Feng Li wrote:
> Dear R,
>
> I have two small questions confused me recently. Now assume I have a matrix
> "a", like this,
>
>> a<- matrix(1:6, 2, 3)
>> a
>       [,1] [,2] [,3]
> [1,]    1    3    5
> [2,]    2    4    6
>
> I sometimes need each row of "a" raised to a different exponent. So I do a
> trick like this,
>
>> a^c(2, 3)
>       [,1] [,2] [,3]
> [1,]    1    9   25
> [2,]    8   64  216
>
> My first question is that if it is possible to do this trick column wise?
> Just out of curiosity, of course I know there are other ways of doing this.
>
> And the second question is why I get such result when I put another element
> in the exponent part like this,
>
>> a^c(2, 3, 4)
>       [,1] [,2] [,3]
> [1,]    1   81  125
> [2,]    8   16 1296
>
>
>
> BTW, I have a 64bit R version (2.11) for Linux. Any advice would be
> appreciated.
>
>
>
> Feng
>

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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